Selecting the Right Telescope
The first time I looked through a large telescope I was seven years old. My father was a rocket scientist, literally, and one of his colleagues at work invited us over to have a look through his very large telescope. At that time Mars was close and visually accessible, so we went over to his house for a look. The telescope was HUGE! I remember to my seven year old eyes it looked like something out of a Jules Verne story. It was made of wood strips with metal staves holding it all together, sort of like a long, skinny barrel. I remember him saying it was sixteen feet long and there were stairs up to a platform where you could see into the eyepiece to view whatever the telescope was pointed at. It also had a very noisy tracking motor on it, as any time you look at a celestial object through a powerful telescope, it will very quickly “walk” out of your field of view due to the earth’s rotation. The tracking motor was designed to move the telescope in the right direction at the proper speed to keep whatever was being viewed in the picture. At such a young age the whole thing gave me the impression of being kind of rickety and cobbled together. After what seemed like forever the target was acquired and, after the grown-ups were done, I was allowed to climb up and have a look for myself at what everyone else had obviously been very impressed by. When I looked into the eyepiece and saw Mars for the first time, it took my breath away. I stared hard into that telescope and was awestruck at the polar icecaps, the “canals” and the reddish tint of the planet. After a few seconds I pulled my head back and looked up in the sky at the little white dot that I had been told was what we were looking at. Everyone got a laugh out of that, and I put my eye back to the instrument until they had to take me down off the step. I was forever hooked.
Since then I’ve gone through several phases of skywatching. After my close encounter with Mars, I wanted to know what everything up there was. I didn’thave any means of acquiring a telescope at that time, but I could look up at the sky and see the stars, planets and constellations. For years I read books about the constellations and what the stories were behind their names. I learned about the seasons by following the stars at night and the sun during the day. When the time was right, I bought a telescope. The first was a cheap (and I mean cheap) refractor, then I started using binoculars and finally I graduated to the large telescope I own today.
This article is designed to help the neophyte astronomer choose the telescope that will serve his interests and desires most closely. Good optical equipment is not cheap, so buying the telescope that will allow you to do and see the things you want is paramount.
The first telescope I looked through that fateful night so long ago was a very large Newtonian reflector. I never got the exact dimensions, but years later my father told me it was two feet in diameter and sixteen feet long. I’m sure those numbers are not exact, but they’re close enough for this conversation, and that brings us to the first point in choosing a telescope:
Aperture is King
Telescopes were once described to me as buckets you catch light in. The bigger the bucket, the more light you’re going to catch. It really is as simple as that. The bigger the aperture, the more light you’ll gather and the more you’ll be able to see. There are a couple of other factors that can slightly mitigate that fact, but the bottom line is, the bigger the aperture the more deeply you’ll be able to see out into space and the more detail you’ll be able to pick out once you’ve acquired an object. Bigger really is better when it comes to telescopes. When considering aperture, remember that the area of a circle grows exponentially. A 6-inch aperture has twice the light gathering capability of a 4-inch aperture. An 8-inch aperture has almost twice as much area as a 6-inch does, and so on. You don't have to go WAY bigger to go way bigger, if you know what I mean.
Now you have to decide what type of telescope you want. There are basically two types of telescopes; refractors and reflectors.
Think of that spyglass the pirate pulls out form under his coat and stretches away from his eye to see if that really IS the British Navy on his tail. That is a refractor. Refracting telescopes have a lens in their primary aperture (the big opening at the front end of the telescope) that catches light and focuses it back through a secondary lens (which the viewer has pressed his eye against) to provide a more detailed, magnified view of a far-away object. Some of the advantages of this type of optics are they typically provide sharper images and the images are upright and oriented correctly left-to-right. Spotting scopes, binoculars and spyglasses are all refractors. Some of the disadvantages with refractors are they tend to have smaller apertures so they can’t see as far out into space at night (smaller bucket, less light captured) and good refractors are EXPENSIVE! Especially big refractors. I used to know a guy with a big refractor and the cost of his tri-pod mounting/tracking system alone was well into five figures.
Reflecting telescopes work just like you’d think. They use mirrors to capture light and focus the image instead of lenses. But it’s not quite that simple because there are a couple of different types of reflectors:
Newtonian Reflector: A Newtonian Reflector has one long tube. At the bottom of the tube is a concave primary mirror that catches light and focuses it onto a secondary mirror about two-thirds of the way back up the tube which reflects the light out the side and through an eyepiece to the viewer’s eye. These telescopes tend to give you brighter images than the others due to larger aperture and no obstructions within the tube. They also tend to be bulkier and harder to transport.
“Folded Optics” Reflectors: There are several different types of reflectors with multiple mirrors that are designed to give you the large aperture of a reflector without the tube length. To put it simply, the bigger the reflector the longer the telescope needs to be to gain the focal length required to focus the image. If you have a 12-inch primary mirror you can’t put the eyepiece one foot away because there isn’t enough room, or focal length, to focus the image. If you put a series of mirrors in the tube, you can “fold” the focal length into a shorter tube. These tend to be pricier than a Newtonian and the images will be dimmer due to the additional mirrors inside the body of the telescope. They’re shorter and easier to transport and also more stable in the wind.
Whatcha gonna do?
Now that you have an idea of the different types of telescopes there are, you have to ask yourself what it is you want to do with your new telescope. This may sound silly, but it’s not. You may buy a reflecting telescope with no tracking system and then decide you want to take pictures. Wrong telescope. You may get seduced by the size advantage and technology of a folded-optics telescope and then be disappointed by the dimness of the image you’re seeing. Oops again. In either case you’re out the money you already spent and you’re starting to think about a different telescope.
As I’ve mentioned already, telescopes aren’t cheap. I knew before I bought my telescope that what I wanted was to see things with my own two eyes. I wanted to know how to locate them in the sky myself and I wanted to know what time of year different nebulae, star clusters, binary stars, etc. were up there for my viewing pleasure. I wanted to learn as well as to see. In short, I wanted my telescope to be an extension of my eyes and brain, not something that took them out of the equation. So when the time came to decide on a scope, those are the things I accounted for. I thought about what I wanted to do and what I didn’t want to do, and so should you. Don’t forget to buy a good field guide for the night sky. You’ll need it.
If what you want is to see and learn about the sky, especially if you are just starting out, get a Newtonian Reflector. By far the most bang for the buck is to be found here as far as aperture and viewing quality. Another plus is you'll need to learn to navigate around the sky to find what you want to see. These telescopes don't typically have computerized tracking/locating systems. It's a great incentive to learn about the night sky. Get the largest one you can comfortably transport and afford. Whether mounted on a tri-pod or Dobsonian mount, these are the simplest to use and will provide the best viewing, inch for inch. They also take up the most room in your car.
If you are interested in photographing deep sky objects (nebulas, star cluster, etc.) and have the budget for it, then you’re going to want to go with a refractor. You will also need a mount that has a tracking motor. The telescope will act as your camera’s lens and the tracking motor will keep the object in focus. This is a very equipment oriented pursuit, so do your homework and bring your checkbook.
If you need something that is compact and easy to transport, then you want to go with a “folded optics” type telescope. These scopes are versatile and can be used for photography and fitted with all kinds of computerized stuff to help you along. They have fancy names like “Schmidt-Cassegrain” or “Maksutov” to name a couple, but they all operate on the same principle. Multiple mirrors within the tube to provide focal length to support a large aperture with a relatively short tube.
Last but not least, if you’re not ready to sink the money into a telescope and you’re looking for something you can use for other pursuits as well as stargazing, there are always binoculars and/or spotting scopes. Some of these are fine pieces of equipment that will allow you to see the night sky well enough to decide if you really want to invest in a good telescope but if not, you can still use them elsewhere.
I hope this article helped you to get some direction in your search for the right telescope. At the very least it should get you doing some research on your own to decide what scope will work best for you. Happy stargazing!